The present invention relates to structure pre-form bodies consisting of open-cell foamed material presenting a comparatively solid framework co-vibrating in a resonant manner at low frequencies as panel lining for wide-band sound absorption.
Structured sound-absorbing panel linings are known for the application in acoustic free-field spaces, which consist of a porous material and present substantially a wedge-shaped or pyramidal geometry [1, 2, 3, 4]. This outside geometry is realized with both compact shaped or pre-formed bodies [1, 2, 3] and also with layers or other element assemblies [4].
The acoustic classification [1] of these panel linings is mainly determined by a frequency-independent high degree of absorption at an orthogonal incidence of sound. The lower critical or limit frequency, from which onwards this high absorption level is reached, is of particular importance because it is decisive for the total thickness of the panel lining. Conventionally structured linings are governed by the relationship that the lining thickness corresponds roughly to one quarter of the wavelength of the lower limit frequency when a 99% degree of absorption is required. This furnishes a lining thickness of roughly 0.85 meters at a lower limit frequency of 100 Hz. In view of this magnitude it becomes evident that a reduction of the lining by roughly 40% saves not only some volume of the structure but also enlarges the measuring radius in the space [5] with an unvaried high degree of absorption.
The present invention is based on the problem of designing the pre-form bodies according to prior art in a way that the structural depth may be made smaller while the acoustic characteristics are retained at a constant level.
This problem is solved by the pre-form bodies according to the present invention.
The pre-form bodies consist of a plane base layer of a defined thickness on the side of the wall as well as a columnar structure positioned directly in front of the base layer and having a defined distribution of height and cross-section in the manner of a wide-band tuned moderator gap. The maximum columnar height corresponds expediently to the thickness of the base and the columns have a one-side bevel cut on a room side whilst the moderator gap has a one-side bevel cut on its base side.